1. Field of the Invention
This invention relates to a latex composition which, after application to a surface and drying, forms a heat-resistant film. More specifically, this invention relates to a latex composition which, when formulated into an ink and applied to a surface and dried, the dried ink exhibits superior heatresistant characteristics.
2. Description of the Related Art
Paper products such as corrugated cardboard frequently require printing for decorative and functional purposes. In some applications, the inks used in the printing operations must form a dried film which is resistant to heat so that subsequent operations such as heat sealing which require that the printed substrate pass through high temperature nips will not smear the ink. U.S.Pat. No. 4,730,019 teaches a coating composition having improved heat resistance, the coating composition comprising a ligand-free monomer maleic anhydride polymer that is able to be solubilized in an aqueous medium, and an effective amount of a metal ion-containing fugitive ligand complex to solubilize the polymer in the aqueous medium, said aqueous medium having a pH of from 7 to 9 wherein the ligand-free monomer is a polymerizable ethylenically unsaturated monomer selected from a group consisting of alpha-olefin, aromatic alkenyl monomer, acrylate monomer, methacrylate monomer and combinations thereof, wherein the metal ion of the metal ion-containing fugitive ligand complex is a zinc or zirconium ion, and wherein the fugitive ligand is ammonia. U.S. Pat. No. 4,730,019 teaches the use of an effective amount of zinc ammonium carbonate to form a solution. This polymer solution, unlike the composition according to the present invention which is a latex, is used in ink formulations for various printing applications. When the composition of U.S. Pat. No. 4,730,019 is used in an ink formulation for printing on paper surfaces such as corrugated cardboard, it does not exhibit the heat resistance necessary for subsequent fabrication operations such as heat sealing. No commercially available printing inks exhibit both acceptable optical properties of gloss and transparency and heat resistance. The latex composition according to the present invention yields a film which exhibits both good optical properties and heat resistance when subjected to elevated temperatures encountered in operations such as heat sealing.